BOONE, Iowa — Delivering stump speeches with more references to the Bible than to the economy, Rick Perry struck out at surging opponent Rick Santorum on Saturday while continuing to paint himself as the socially conservative candidate religious Iowans are looking for.

“I ask you to join me in echoing the words of the prophet Isaiah: ‘Here I am, send me,’” he told voters in central Iowa, where his brightly painted tour bus bearing the slogan “Faith, Jobs and Freedom” stopped at Bloomers Coffee Shop in Fort Dodge and The Gigglin’ Goat reception hall in Boone.

Struggling to break into the top tier of candidates, Mr. Perry has lately tried to transform his campaign image from the job-creating Texas governor to that of a Washington outsider who values faith, protects life and wants to limit government.

The tactical shift hasn’t lifted his lagging poll numbers. They seem to have slipped in the opposite direction according to a Des Moines Register poll released Saturday night showing Mr. Perry with 11 percent support among likely caucusgoers, in fifth place behind Newt Gingrich.

Nonetheless, he has launched a frenzied ground campaign in the final hours, bringing in more than 450 out-of-state volunteers and appearing around the state with his family in tow—his wife, Anita, daughter Sydney, son Griffin and daughter-in-law Meredith.

As Mr. Perry remains stuck near the bottom of the pile, he’s directing nearly all of his attacks at Mr. Santorum. The two-term U.S. senator’s conservative record on abortion and gay-rights issues offers little room for criticism, but Mr. Perry sees opportunity in Mr. Santorum’s votes for federal earmarking and raising the debt ceiling.

“You gotta ask yourself, if we replace a Democrat insider with a Republican insider, you think Washington D.C. is going to change any?,” he said. “It’s not.”

He reminded the voters that most of the top candidates have spent time in Congress—a combined 63 years, he said, presumably referring to the terms served by Mr. Santorum, Rep. Ron Paul, Rep. Michele Bachmann and former House Speaker Newt Gingrich.

And he flashed his own credentials on social issues at every opportunity, prompting especially enthusiastic applause when he mentioned signing a bill last summer to defund Planned Parenthood in Texas.

When asked whether he believes abortion should be legal in the case of rape or incest — exceptions that are generally included in federal anti-abortion legislation — he spoke of meeting a woman born out of rape who shifted his thinking.

“She looked me in the eye and said, ‘is my life not worth saving,’” Mr. Perry said. “And at that particular point in time, she really had an impact on me that if you’re truly going to be standing up for life, having only the exception for the life of the mother is appropriate.”

He also played to his audience with the biblical references, even managing to derive some joke material from the Good Book.

Opening his speech at The Gigglin’ Goat, he told voters that he had visited The Fainting Goat in Waverly the day before.

“With all the goat stops along the way, the parable from the Bible came to me about separating the sheep from the goats,” he said, winning some chuckles from the crowd.

Voters at both events asked Mr. Perry about his support of legislation allowing undocumented immigrants who live in Texas to obtain in-state tuition rates—questions that he turned into a chance to rail on the federal government’s struggles in securing the Mexico border.

“The president came to El Paso this year and said the border was safer than it’s ever been in history—I thought he was talking about the Canadian border,” he quipped.

Compared to smooth-talking candidates like Mitt Romney and Newt Gingrich, Mr. Perry’s speeches can come across as somewhat choppy and hesitant. But he seemed to connect with the voters when he spoke of his rural upbringing in the tight-knit community of Paint Creek, Texas.

Growing up in Paint Creek wasn’t so different than growing up in Iowa in the mid-1950’s, he told the crowded room at Bloomers Coffee.

“The president of the school board was also the suprerintendent of the Sunday school and was also my scout master,” he said. “My football coach was the civics teacher, he was the principal of the high school, he was the basketball, track and football coach and he also drove the school bus.”